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The Spruce Budworm 
and Larch Sawfly 



Lecture delivered by Dr. C. Gordon Hewitt, F. E. S., Dominion 

Entomologist, at the Canadian Forestry Convention, 

City of Quebec, 1 9th January, 

1911. 

Reprint from the Report. 



The British Whig Publishing Co., Limited, 

Kingston, Ontario, 

1911. 



THE SPRUCE BUD WORM ND LARCH SAW FLY 

Dr. C. Gordon Hewitt, F.E.S., Dominion Entomologist, Ottawa. 

During this convention forest conservation has been fully discussed, but thi. 
discussion has been more or less limited to the consideration of one factor in 
forest destruction — fire. What has struck me is the fact that except for two 
references, in almost as many words, there has been no mention of another great 
destructive agency, namely insects. This seems peculiar when you think of one 
insect which when it appeared first (1882-6) destroyed all the mature tamarack 
from Nova Scotia to Winnipeg. When we have such an insect spreading more 
destructively than any fire, because it is selective in its destruction, it is quite un- 
intelligible to me why there should be this apparent neglect of this factor. You 
will observe that I say apparent neglect, because I do not think there is any real 
neglect on the part of those interested. 

In this matter we cannot consider one factor to the exclusion of the others. 
The three factors chiefly responsible for the destruction of our forests — fire, 
insects and plant diseases, are all closely interrelated. Possibly the reason that 
insects are not generally mentioned is because, working as they do quietly and in- 
sidiously, they carry on their destruction unnoticed except by the expert who is 
trained to detect them ; whereas a fire can be observed by the smallest child and 
its ravages cover a large area in a very short space of time. 

I believe that in Canada we suffer quite as much in the aggregate from in- 
sects as from fire. It has been estimated by the United States Department of 
Agriculture that the annual loss in the forests of that country through destructive 
insects amounts to over $65,000,000. This is figured from actual observations 
in the forests covering a period of at least ten years. You can thus realize the 
enormous loss caused by insects which we shall have to consider as affecting 
first, the growing timber; secondly, timber products; and thirdly, the second 
growth upon which the perpetuation of the forest depends. 

Twelve months ago at the first meeting of the Commission of Conservation I 
| called attention to the important relation that insects bear to forestry in Canada 
(and to the conservation of our forests, and the urgent necessity of studying all 
.the facts possible concerning insects bearing upon this relation. I am now ad- 
dressing a body of men most of whom are concerned in the practical aspect 
I of forestry, and to you I repeat with increased emphasis that as insects play so 
large a part in the destruction of forests, the increasing importance of our 
' forests as sources of timber, for regulating the water supply, for preventing 
erosion and for the other objects with which you are all familiar, will make it in- 
creasingly essential that, by careful scientific investigation, we shall be in pos- 
session of these facts concerning the life-histories, habits and natural means of 
:ontrol and other factors upon which alone any measures of control can be based 
and recommended. 

It is not my intention to retrace my steps over the ground which was 
traversed in my previous address. I was requested to speak to you upon two in- 
sects which have had and are at present exercising a serious influence upon some 
of our important forest trees : the sawfly which is attacking the larch or tamarack, 
and the spruce bud worm whose attacks upon the spruce and balsam in the pro- 
vince of Quebec have been the cause of much alarm on the part of those interested 
in the timber and pulpwood limits. 

Both of these insects belong to a class which is destructive by reason of the 
larvae defoliating the trees, and this class of insects is not so serious in its results 
as the group of bark beetles, which are responsible for enormous damage to coni- 
ferous trees as the records of the investigations in the United States show 
Nevertheless, I shall be able to show you that under certain conditions de- 
foliating insects may be the primary cause of most serious losses. 



M The S. :e Budworm. 

The insect which is causing n jst alarm at present in the forests of the 
evince of Quebec is the spruce budworm (Tortrix fumiferana, Clemens). Its 
epredations were first reported to us by the Hon. W. C. Edwards in 1909, as it 
was defoliating considerable areas of balsam and spruce in the upper Gatineau 
region about 100 miles north of Ottawa. It was also repotted as defoliating the 
Douglas fir in British Columbia. During the past season a large number of re- 
ports and enquiries have been received by the Division of Entomology con- 
cerning the defoliation of spruce and balsam in Quebec and o£ the Douglas fir 
on Vancouver Island. As the Department of Lands and Forests of the govern- 
ment of the province of Quebec has a body of forest rangers throughout tl.e 
province, arrangements were made by Mr. G. C. Piche, Chief Forestry Engineer, 
to obtain reports from them as to the distribution of the insect, and we drew up 
a list of questions. The results of this inquiry and of the information which the 
Division of Entomology has received indicate that the insect is abundant in cer- 
tain areas from Lake Timiskaming on the west to Lake St. John on the east and 
is sparingly distributed throughout the whole province down to the International 
boundary. The most serious devastations have been recorded from the region 
having River Desert and the Upper Gatineau on the west to the Rouge River 
and Lake Ouareau on the east ; from the region southeast of Lake St. John ; and 
from the River St. Maurice. In British Columbia, where I visited the infested 
areas last year and again this year, the most severely infested region is the south- 
east region of Vancouver Island from Salt Spring Island and Maple Lay south 
to the Saanich Peninsula. Dr. Fletcher recorded it from Manitoba in 1907, and 
immature caterpillars which appeared to be the spruce budworm were sent to the 
Division during the past summer from Brandon, Manitoba. In Quebec it is 
attacking chiefly the balsam and spruce, but specimens attacking larch and white 
pine were also received from the River St. Maurice. In British Columbia it is 
defoliating the Douglas fir and in severely infested localities it will attack other 
conifers such as hemlock, larch, silver fir, &c. As its name implies its cater- 
pillar feeds upon the buds of the tree, destroying these and thus preventing 
the further growth of that shoot. After the destruction of the bud it turns its 
attention to the leaves or needles which are eaten off at their bases after spinning 
them together by means of silk, the caterpillars thus make loose shelters in which 
they live. These dead leaves and the defoliated twigs, together with the excreta 
or frass formed by the caterpillar, give the branches their characteristic reddish 
brown appearance so that an infested forest seen from a distance appears to 
have been swept by fire. The life-history of the insect is of interest. The win- 
ter is passed in the caterpillar stage, as a very small caterpillar, we believe, in a 
little shelter constructed near a bud. In the spring, when the bud begins to swell 
the caterpillar begins to feed and becomes full-grown towards the end of May 
and beginning of June. They are then four-fifths of an inch long, of a reddish 
brown color, and have small light yellow warts on each segment of the body ; the 
sides of the caterpillar are lighter in colour. They transform into brown chrysalids 
inside the loosely-made shelters. In six to ten days the small brown moth emerges 
from the chrysalis dragging the empty case partially out of the larval shelter. The 
moths are found from the middle of June to the end of July. Shortly after emer- 
gence they deposit their peculiar pale-green scale-like eggs in small oval patches 
on the undersides of the needles, and they are not conspicuous. The eggs hatch 
in about a week or ten days and the young larvae feed for a short time on the 
terminal shoots of the branches before hibernating. During July, when the moths 
are flying, they occur in enormous numbers about the electric and other light's. 
This has been specially noticeable in Ottawa, Quebec, and in Victoria, B. C. 
They are carried considerable distances by the wind, and this method of dispersal 
accounts for the rapid spread of the insect. The result of our inquiries would 
indicate that the spread of the insect has been in the direction of the prevailing 
winds at the time of the year when the moths are flying. 



The results of the attacks of this insect,, though a defoliating insect, are serious, 
though they are more complex than w0uld appear at first signt. P ckard stated 
that the destruction of the spruces along the Maine coast in the -early 'eighties' 
was chiefly due to this insect. It is not unlikely, however that the bucforim was fol- 
lowed by other insects. The primary injury is to the buds which are ftcstroye 
and thus the growth is checked — a serious matter on a slo\vly-gro\ving tr€ 
The repeated defoliation weakens the vitality of the tree with the result that 
reaches a certain point at which it is susceptible to the attacks of bark-beetle 
the chief of which is the Eastern Spruce Beetle (Dendroc tonus piceaperda Hop 
This beetle is more serious in its effects than any other enemy of the spruce, a„ 
it kills the tree which is then readily attacked by timber borers and fungi. As 
Hopkins has stated this species of bark-beetles has caused the death of a very 
large percentage of the mature spruce over an area of thousands of miles 
in the spruce forests of New York and the New England States and southeastern 
Canada. It has been found killing the mature spruce in Quebec, New Brunswick 
and Nova Scotia. The greatest danger to my mind, therefore, of the present 
outbreak of the spruce budworm in Quebec is not so much the direct killing of the 
trees by repeated defoliation but the reducing of the vitality of the trees and 
rendering them more suspectible to the attacks of bark beetles especially the 
spruce beetle which is present in many of the affected localities, and one of m> 
chief objects in making a tour of inspection of the most severely infested 
localities will be to discover whether the trees are being weakened in vitality, 
and this secondary attack of bark beetles is taking place. That the spruce bud- 
worm is able, however, to cause the death of the trees directly is demonstrated 
in British Columbia where it has killed a considerable quantity of the young 
Douglas firs of the second growth which is a most serious matter as affecting the 
natural regeneration and afforestation. 

Spreading like fire by means of the moths it is impossiole to check tie spread 
of this pest by ordinary means. Two things only appear to be possible ; to study, 
in the manner I describe later in my account of the larch sawfly, the progress 
of the work of the parasites with a view to ascertaining whether the natural means 
of control are proving effectual and, by careful inspection of the infested areas, 
to detect the beginning of the attacks of the bark-beetles upon the weakened 
trees. As soon as such attacks are observed the trees should be immediately 
dealt with, as is possible in the early stages of the outbreaks of these insects. By 
such timely action it may be possible to prevent the spread of the beetles and 
the weakened trees, instead of being killed by the latter, will have the opportunity 
.o recover, should the outbreak of the budworm be transient or checked by 
natural causes. These bark beetles are the most destructive of all insects at- 
tacking conifers but, at the same time, if the necessary steps are taken, it is 
possible to prevent serious outbreaks. The chief essential is that the forest rangers 
shall have such entomological knowledge as will enable them to detect the first 
signs of the outbreak the chief of which is the turning yellow or red of the tops 
of the trees. The presence of the spruce budworm will make such detection 
more difficult. If the identity of the species of beetle is scientifically determineci, 
it is usually possible to recommend the measures to be taken to check the further 
spread of the insect. 

A study of the parasites of the spruce budworm, both in Quebec and British 
Columbia, is being made with a view to ascertaining the extent of their work. 
This insect is stated not to have many parasites. So far, we have discovered 
about seven species of parasites which attack it, and next year we hope to have 
sufficient material to enable us to estimate the degree of parasitisation. 

The Larch Sawfly. 

This 'larch-worm,' as it is sometimes called, since the defoliation of the larch 
or tamarack is caused by the caterpillar, has been known in Europe since the early 
part of the nineteenth century where it was injurious to the European larch in cer- 



tain regions of Germany. /it was first discovered in America by Dr. Hagen of Har- 
vard University who recorded it in the^'Canadian Entomologist' in 1881. In that 
and the two following years it was found through the New England States where 
great destruction of the larch was caused. It was not long in reaching Canada, for 

n 188? i>r. Fyles reported its appearance in Quebec on Larix Americana. Two 

^ars later, my predecessor, Dr. Fletcher, gave an account of its occurrence in his 
mual report as Dominion Entomologist: it occurred throughout the east in the 

rovinces of Ontario, Quebec, New Brunswick and Nova Scotia. In 1905 it 
ain assumed serious proportions and it will be of interest to quote Dr. Fletcher's 

eference to it in his report of that year. After mentioning the fact that it 
reached Canada in 1882, he states that after three or four years of being stripped, 
the larches over millions of acres, and practically over the whole of Eastern 
Canada, were wiped out. With this large destruction of its food plant, the insect 
practically disappeared until 1904 when it again become noticeable upon 
ornamental European larches and on larches in swamps. Further, he 
says: 'A feature of the last outbreak of 1882 to 1885 was the rapidity 
with which the attack spread, and the suddenness with which it disappeared. 
Occasionally specimens of the saw fly or of the colonies of larvae have been seen 
from time to time since 1885, but there has been no noticeable destruction until 
the present year.' This last attack has now spread along the forest belt into 
Manitoba where I have observed it during the past two years, and it has also 
been reported from near James' Bay and recently as far west as Battleford, 
Saskatchewan. I have not found it attacking the western larch in British Col- 
umbia, but its occurrence there would not be surprising. East of Winnipeg it 
may be said to extend to the Atlantic as I have found it throughout to the eastern 
region of Nova Scotia. Its present known distribution in Canada, therefore, is 
over an area of 2,500 miles in extent. In the United States it extends from the 
Atlantic coast to Minnesota and as far south as Pennsylvania. 

The results of the first outbreak were disastrous as was seen from the report 
just quoted. The second growth of larch is now being attacked, and we cannot 
prophesy as to the result of this renewed outbreak. Even should these trees escape, 
I shall show later in what manner the timber has been reduced in value and utility 
in most cases by the effect of the first visitation of 1882-5 upon the young second 
growth. 

The habits and life-history of the insect are such as to render it injurious in 
both the caterpillar or worm stage and the fly stage. The winter is passed by the 
larva in a cocoon under the turf round the base of the tree. In May the larvae 
.transform into the perfect insect and the flies begin to emerge during that month. 
An interesting feature of the productive powers of the larch sawfly is that it can 
reproduce parthenogenetically, this means that the females can deposit eggs 
which, although they have not been fertilized by the males, are not infertile but 
produce larvae of the sawfly. This interesting phenomenon which also occurs in 
certain other insects, is of importance as the productive power of the species is 
increased when the necessity of the female meeting a male is dispensed with. 
Shortly after emerging the females begin to deposit their eggs. The eggs are 
always deposited in the terminal green shoots of the larch and never on any other 
part of the tree. In laying the eggs the female sawfly makes an incision in the 
tender stem of the shoot by means of a pair of saw-like instruments at the end 
of the body and into this incision the egg is pushed. The eg^s are usually d 
posited in a double row in the shoot and as many as forty or fifty eggs may be 
found on a single green shoot. As they are usually deposited along one side of 
the shoot the injuries inflicted by the saw-like appendages of the female cause 
the shoot as it grows to curl. In many cases the injuries are so severe as to kill 
the shoot and the presence of the dead and reddish-brown shoots often serves as 
an indication of the presence of the insect. In about a week to ten days after 

deposition the eggs hatch and the young pale green caterpillars emerge and im- 
mediately begin to feed upon the green verticels of leaves. As they become older 
they feed in masses, sometimes as many as fifty or sixty caterpillars in a single 



cluster and, feeding in this manner, they pmpletely strip the branches of ail 
green leaves which gives the trees a. winter i. jpect in the middle of summer. The 
caterpillars are full-grown in three to four Veeks and, during their 1 ^es, the 
cast their skins five times. As the period during which the sawfiies em rge from 
the cocoons is a lengthy one, there is a correspondingly long period auring 
which the eggs are deposited and the larvae emerge; in consequence o; this, one 
may find recently-emerged caterpillars feeding side by side with iull-grovvn 
specimens and the caterpillars may be found in Canada feedi -g as late as the 
second week in August. As the first newly hatched caterpillars were found 
during the last week in May in the neighbourhood of Ottawa and full-grown 
caterpillars in August, and as the caterpillar stage is not a long one, it might 
be assumed by anyone who had not made these observations that there were two 
broods of the sawfiies during the year, which has been proved not to be the case. 

The full-grown caterpillar measures about two-thirds of an inch in length. 
Its color is bluish or glaucous green, the lower surface being a lighter green. 
The head and three pairs of thoracic legs are jet black. It also possesses seven 
pairs of abdominal legs. When the caterpillars are full-grown they either crawV 
down or drop from the tree and penetrate the turf round the base of the tree 
to the depth of a few inches. There they spin a brown oval cocoon about two- 
fifths of an inch in length, and in this the winter is passed, the caterpillar trans- 
forming into the perfect insect in the following year as previouslv described. 
The sawfiies are black with the middle portion of the hind-body or abdomen a 
bright resin-red and they measure about half an inch in length. 

The forester is naturally most concerned in the measuies which may be 
adopted to control or prevent the attacks and spreading of a pest. Means of 
control are of two kinds, those of nature and those of man; the latter are fre- 
quently adaptions of the former. In cases where a pest has gained some headway 
and extends over a large area, especially of virgin forest, it is normally impractic- 
able to adopt any measures of control which will be of value. We are compelled 
to wait the disappearance of the pest either by the exhaustion of its food 
supply by the killing of the trees or bv its extermination through th^ attacks of 
parasites or other natural enemies. For this reason the study of Ihe natural 
means of control is attaining- considerable importance in entomological problems 
and mention will be briefly made of such a study which I have been making 
during the last few years in connection with the outbreak of this insect in 
England and in Canada. In that investigation it was found that the commonest 
parasite attacking the caterpillars of the sawfly in England was an Ichneumon 
Ifesohius aulicus and it was decided to study the progress of the work of this para- 
site from year to year. In 1908 it was found that it had attacked and destroyed 6% 
of the caterpillars of the previous year. Next year the percentage of caterpillars 
killed by the parasites was 15% and last year the percentage of caterpillars killed 
by this natural means of control was nearly 65%. an enormous increase which 
means that the parasite has practically gained control over the sawflv. and this 
is borne out by the observations made by Mr. Mangan who is continuing the 
work, who informs me that during the past summer the trees, instead of having 
the completely burned appearance and defoliated condition of the previous years, 
had the normal green appearance, so it was not a little difficult to discover the in- 
sects. This disappearance was almost entirely due to the natural causes, the 
chief of which was the parasite Mesoleius aulicus. The chief of the other 
potent natural causes were the small voles or field mice and the birds, especially 
the tits. A system of bird encouragement and protection was initiated when it 
was discovered that certain species of birds were feeding upon the caterpillars, 
especially as there was a relative scarcity of birds in the infested region. Nest 
boxes were distributed, an additional number being provided each year. Last 
vear there were nearly 300 boxes and over 50% of these were occupied, which 
indicates a considerable increase in the number of birds in view of the scarcity 
previous to their encouragement. Such a system of bird protection, in other 




LIBRARY OF CONGRESS 




words the encouragement of the na # . ^ enemies of these insert j _ 

on in Europe not only by individuals at also by those states in which the forests 

are important natural resources. 

This study of the parasitic an , other means of natural control is the only 
line of investigation which can be carried on and its practical results, although 
they may not b£ apparent at first sight, are nevertheless of importance as we 
can measure the efficacy and progress "of natural causes of control, and in this 
way alone can/prophesy the course that the outbreak will take, which will enable 
the forestej^fo act accordingly. During the last year a beginning was made of 
^a^tuc^roTthe parasites of this sawfly in Canada, the chief of which was found 
to be a small insect Coelopisthia nematicida Packard, which deposits its eggs in- 
side the cocoon by piercing the cocoon with its elongate ovipositor. . The eggs 
are deposited on the hibernating caterpillar lying inside the cocoon and on hatch- 
ing the parasitic larvae feed upon it and so destroy it. From the prevalence of 
this parasite which has been reared from cocoons found not only near Ottawa 
but also from Massachusetts, I am inclined to consider it an important factor in 
the natural control of the pest. 

The serious result of the attack of this insect does not consist in the des- 
truction of the mature timber alone, but also in its effect upon the young second 
growth. I have previously shown how the injury to the young growing shoot 
by the female in inserting her eggs may either kill the shoot or cause its cur- 
vature and it may be so strong as to cause the shoot to curve through a complete 
circle. Usually, however, a strong curve in the stem is formed and an erect position 
is gained subsequently. This strong curve or kink on the stem has a serious effect 
on the growth of the timber, and as a result of these injuries you may see the 
young larches from Cape Breton, Nova Scotia, almost to Winnipeg having the 
main stem curved in various ways, as my illustration shows, rendering the 
future timber totally insuitable for the best uses to which the larch is put. The 
results of this insect's work, then, are twofold, the killing of the mature trees by 
repeated defoliation and the permanent injury to the young second growth which 
enormously reduces the value of the subsequent timber and ifl this manner not 
only is the larva injurious but the mature insect also. As in the case of the 
spruce, the trees weakened in vitality by defoliation by the caterpillars will be 
especially subject to the attacks of the bark-boring beetles and also of those fungi 
to which the larch' is susceptible. 



The Chairman — I am sure that as Canadians we will all congratulate our- 
selves that we have a Minister of Agriculture who has the good sense to profit 
by the scientific assistance of such men as Dr. Hewitt. I am also sure that every 
one of us feels regret that our good friend. Senator Edwards, was not here to 
appreciate what science can do in a practical way for the development of the 
forestry industry. Personally I do not know when I have enjoyed a lecture as 
much as I have enjoyed Dr. Hewitt's address. I trust! we shall have an oppor- 
tunity of hearing him asrain at another meeting of our Association, for I feel 
that such addresses as his cannot but be of benefit to us individually and as 
an organization. v 

It being 10 p.m. the convention adjourned. 



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